Method for solvent extraction of oil



June 7, 1938. u. B. BRAY METHOD FOR SOLVENT EXTRAQTION OF OIL FiledMarch 21, 1934 I INVENTOR. ZIZrzc5.Bray BY I Mr ATTORNEY.

Patented June 7, 1938 UNITED STATES METHOD FOR SOLVENT EXTRACTION OF OILUlric B. Bray, Palos Verdes Estates, Calif., as-

signor to Union Oil Company of California,

Los Angeles, Calif., a

Application March 21,

6 Claims.

This invention relates to a process for the treatment of petroleum withselective solvents. Although it may be employed for use with otherpetroleum fractions, it is especially applicable to the treatment oflubricating oil.

In the production of lubricating oil for internal combustion motors itis highly desirable to obtain a product which exhibits a low temperatureviscosity susceptibility, a low Conradson carbon residue value, a highstability towards sunlight and a low oxidation value. Crude lubricatingoil fractions produced either as distillates or as residues are usuallycomposed of mixtures of paraifinic, naphthenic, aromatic and olefinichydrocarbons. The olefinic hydrocarbons are highly unsaturated and theirpresence in the finished lubricating oil is undesirable because of theirunstable characteristics. These compounds are unstable and usuallydarken when exposed to sunlight. tendency towards polymerization withthe result, after a considerable period, that these compounds areconverted into resinous substances which increase the sludge value ofthe oil.

The aromatic and naphthenic hydrocarbons present in crude lubricatingoil fractions are undesirable because these compounds exhibit too greata change in viscosity for a given change in temperature. The. paralfinichydrocarbons present in crude lubricating oil fractions are the mostdesirable materials to be employed as lubricants. These compounds arehighly saturated hence, from a chemical standpoint, they are ratherinactive and do not exhibit a tendency towards the formation ofundesirable resinous or sludge-forming constituents. Furthermore, thesecompounds exhibit a low temperature viscosity susceptibility. In otherwords, they exhibit a minimum change in viscosity for a given change intemperature. Furthermore, these highly saturated hydrocarbons arerelatively stable to sunlight, exhibiting little tendency towarddiscoloration or sludge formation. When I use the term paraffinichydrocarbons I mean those compounds which are present in petroleumhaving the aforementioned characteristics and which are liquid atordinary temperatures. This group of hydrocarbons does not include thosecompounds present which are usually solid or semisolid at ordinarytemperature and which are known as wax or petrolatum.

A further indication of the purity of a lubricating oil is its viscositygravity constant. This constant represents the paraifinicity ornaphthenicity of an oil. A highvalue represents a Furthermore, they havea high corporation of California 1934, Serial No. 716,581

high degree of naphthenicity while low values indicate relativelygreater paraflinicity. Lubricating oils from natural crudes range from0.903 viscosity gravity constant for an extreme Gulf Coast type to 0.807for an extreme Pennsylvania type, or even beyond. The viscosity gravityconstant referred to in this application has been,

determined by the method employed by Hill and Coates as set forth in theJournal of Industrial and Engineering Chemistry, vol. 20, page 641 of1928.

As a matter of convenience hereafter I will refer to those constituentsof petroleum characterized by relatively low viscosity gravity constantas the parafiinic hydrocarbons, and to those constituents of petroleumcharacterized by relatively high viscosity gravity constant, as thenon-paraffinic constituents of petroleum.

In the production of lubricating oil from crude petroleum residues ordistillates, it is becoming conventional in the art to separate thedesirable parafiinic hydrocarbons from the undesirable olefinic,naphthenic and/or aromatic compounds by the use of solvents whichselectively dissolve the undesirable hydrocarbons present in thepetroleum fraction but which exhibit only a very limited solvent poweron the desirable paraflinic hydrocarbons.

A number of selective solvents have been found desirable to separate theparaflinic from the nonparafiinic hydrocarbons, for example, it has beenshown that such materials as sulphur dioxide, beta beta dichlorethylether, chloraniline, nitrobenzene, aniline and furfural are highlyselective as the solvents for the non-paraifinic hydrocarbons. Theforegoing selective solvents are relatively heavy as compared topetroleum. When these relatively heavy solvents are commingled withpetroleum or petroleum fractions under the proper conditions oftemperature, the undesirable non-paraffinc hydrocarbons present passinto solution to a greater or less extent but the desirable paraifinichydrocarbons remain largely undissolved. If the commingled mass isallowed to remain in a quiescent state the solution of undesirablehydrocarbons and solvent settles to the bottom of the container andforms what is known as an extract phase. The relatively lightparafi'inic hydrocarbons rise to the top of the vessel and form araflinate phase. These phases are then readily separable by ordinarydecantation means. The rafiinate phase is usually found to contain asmall quantity of the selective solvent and the extract phase ordinarilycontains a relatively large quantity of the solvent. These fractions maybe purified by subjecting them to distillation whereby the solvent isdistilled away from the hydrocarbon oils.

Due to the general similarity of the various hydrocarbon components ofmineral oil fractions such as lubricating oils, solubilities of theundesirable, non-parafllnic fractions and the desirable paraffinicfractions in a selective solvent usually differ only in degree, andthere is, therefore, a tendency for desirable, high grade paraffinic oilto be carried away with the extract resulting in a loss in the yield ofparaffinic fractions obtained. In other Words, in a phase separation ofextract and rafrlnate fractions from mineral oil employing a selectivesolvent, an equilibrium of paraifinic components as well asnon-paraflinic components is established between the phases.Consequently, some of the desirable paraiiinic fraction is found in theextract instead of in the rafi'inate.

While some loss may occur in a primary extraction of lubricating oilwith a selective solvent for the production of a low grade primaryextract and a primary rafiinate, the loss of desirable paraffinicfractions in the extract is especially severe when the raflinateproduced by the primary extraction is further treated by a selectivesolvent to produce a high grade raffinate and an intermediate gradeextract. In the production of a low grade primary extract and a primaryrafiinate in the first extraction, the difference in solubility of therespective oils is usually so great that commercially satisfactoryseparation is obtainable. In some cases, however, such a process resultsin a substantial loss of parafiinic components in the low grade extract.The difference in solubility between the intermediate grade extracts andhi h grade railmate produced by a succession of extractions is usuallynot so great and there is, therefore, more tendency for paraffinic oilto be carried away with the intermediate grade extracts.

It has been proposed to regulate the solvent power of the extractingagent at any stage of the treatment in accordance with the solubility ofthe material to be extracted and as the refining of the stock byextraction progresses in a stepwise manner, the solvent power of thetreating agent may be increased. 7

By substantially increasing the solvent power or ease of miscibility ofthe treating agent, it is possible to fractionate the raflinate obtainedafter extraction with the pure solvent into a further extract of lowersolubility than the first extract obtained by the use of said puresolvent and a second raffinate of consequently lower solubility than thefirst raffinate. This may be accomplished by first extracting ahydrocarbon mixture with a pure selective solvent, for instance one ofthe solvents set forth above, and then to retreating the raffinate soproduced with a modified solvent. As modifying agents such materils ascarbon bisulphide, xylene, benzene, toluene, carbon tetrachloride,ethers or tetrachlorethane may be employed with the selective solvent.

By these processes the oil feed is divided in one general operation intothree or more fractions of different viscosity gravity constants. Aspreviously stated, the successive extractions produce a high graderaffinate and intermediate grade extracts characterized by solubilitieswhich are not very different from each other. Consequently, in ordinarytreatment of mineral oil by successive extractions, a substantialportion of the paraffinic fraction is soluble in the extract-solventmixture rafiinate by rectifying the phases.

and is lost therein, resulting in a corresponding loss in yield ofdesirable high grade rafiinate.

It has also been proposed to regulate the solvent power of theextracting agent at any stage of the treatment by controlling thetemperature at which the extraction takes place. For instance, thetemperature at which the primary extraction takes place may berelatively low in order to reduce correspondingly the solvent power ofthe solvent. The low grade extract thus produced may then containsubstantially only the highly aromatic and most soluble fractions of themineral oil. Subsequent to recovery of the primary raffinate from thelow grade extract, the former may again be solvent extracted at a highertemperature than that which prevailed in the primary extraction. Theextraction at higher temperature may be accomplished by the same solventas that used in the primary extraction or a solvent of greater or lesssolvent power than that employed for the first extraction may be usedfor the second extraction. These successive extractions likewise producea high grade rafiinate and intermediate grade extracts having relativelysimilar solubilities and consequently substantial quantities ofdesirable paraffinic components are lost in the extract phases. Suchloss also occurs when mineral oil is successively extracted with thesame solvent at the same temperature.

It is an object of my invention to retain the desirable, high gradeparafiinic fractions in the raffinate produced by solvent extraction ofmineral oils.

The paraffinic fractions may be retained in the This may be accomplishedin a series of successive extractions by interrningling the extractphases with raffinate phases of low content of paraffinic constituents.The equilibrium established in the phase separation of these mixtures issuch that the parafiinic content of these extracts tends to bere-distributed into the raffinate phase. When an oil is recovered as arejected raffinate from the extract phase by cooling, it may bere-introduced into the extraction system for rectification purposes.

I have found that when oil is countercurrently extracted with aselective solvent and the extract phase therefrom is cooled to reject anintermediate rafiinate, this intermediate raffinate is characterized bya viscosity gravity constant intermediate that of the raflinate' andextract respectively produced by the extraction. It is an object of myinvention to aid the rectification of the oil dun'ng extraction, and topromote the recovery of paraffinic fractions in the raffinate byintroducing this rejected raffinate of intermediate quality into theextraction system preferably into that zone which contains oil ofsubstantially similar characteristics. The equilibrium in the variouszones of the countercurrent extraction is thus maintained.

I have also found that when oil is first extracted in a primaryextraction zone to produce an ex-' Therefore, it is a further object ofmy invention to extract an oil with a selective solvent, separate araifinate insoluble in the solvent from the extract phase, extract therafiinate with a selective solvent to produce a final raifinate and anintermediate extract phase, remove the selective solvent from theintermediate extract phase and introduce the intermediate extract intothe first mentioned extraction.

Referring to the drawing, the figure is a diagrammatic view of one typeof apparatus suitable for carrying out my invention.

In the apparatus shown in the figure, oil is introduced into primaryextractor I i! by pump II in line I2 controlled by valve I3. Line I2connects with orifice mixer I4 which in turn communicates with extractorI0 via line I5. Selective solvent is introduced into extractor I0 bypump IS in line H controlled by valve I 8. Extract phase is removed fromextractor I0 via line I9 controlled by valve 20. Rafiinate phase from I0passes by action of pump 2| through line 22 controlled by valve 23.

Extractor I0 is divided into a number of sections 26, 27, and 28 byimperforate plates 20. Each section in turn is divided into a mixingzone 30 and a settling zone 3| by plate 32 provided with port 33. Eachmixing zone may be provided with an agitator if necessary, I prefer tointroduce the selective solvent into the uppermost section 26. Rafiinateis removed from this section by line 22 as described. Extract phase fromsection 26 is removed therefrom by pump 35 through line 36 controlled byvalve 37 and is intermixed with the raftinate produced in a lowersection of the extractor. This mixture passes through line 38, orificemixer 39 and line 25 into the mixing zone 30 of section 2?. From thismixing zone the mineral oil mixture and solvent passes through port 33into settling zone 3|. The raffinate from the settling zone of section2'! is removed therefrom by action of pump 45 and passes via line 46controlled by valve 4'I into contact with the solvent entering extractorI0 via line II. This mixture passes through orifice mixer 48 and line 49into section 25.

The extract phase produced in section 2'! is removed by pump 50 throughline 5| controlled by valve 52. Line 5| connects with oil feed line I2,and the mixture of extract, solvent and feed passes through orificemixer I4 and line I5 into section 28 in the manner previously described.The mixture passes through port 33 into settling chamber 3| of section28 and the rafiinate separated therein is passed by pump 5-3 throughline 54 controlled by valve 55. Line 54 joins with line 36 and thecommingled material passes through line 38, orifice mixer 39 and line 40into section 27 in the manner previously described.

Rafiinate from extractor I0 passes through line 22, orifice mixer 56 andline 51 into second extractor 60. Extractor 60 is also divided into anumber of sections 6| to 65 by plates 29 and each section is dividedinto a mixing zone 30 and settling zone 3| by plate 32 provided withport 33. Selective solvent is introduced preferably into the uppersection 6| of extractor 60 by action of pump I0 in line II controlled byvalve I2. Line 'II connects with orifice mixer I3 which in turncommunicates with extractor 60 via line I4. Extract phase from sections6|, 62, and 63 are removed therefrom by action of pumps I5 through linesI5 controlled by valves TI and passed to the next lower sectionsrespectively via lines I8, orifice mixers I9 and lines 80. Rafiinatephases from sections 63, 64, and 65 are passed by action of pumps 8|through lines 82 controlled by valves 83 into the next upper sectionsrespectively by passage through lines I8, orifice mixers I9 and lines80. Extract phase from section 64 is removed therefrom by pump 85through 1ine86, controlled by valve 81. Line 86 connects with line 22and the mixture is passed into section 65 of extractor 60. Rafiinatephase from section 62 is removed therefrom by action of pump 90 throughline 9| controlled by valve 92. Line 9| connects with solvent admissionpipe II and the mixture travels through orifice mixer I3 and line I4into section 6| of extractor 60.

Final raffinate is removed from extractor 60 via line 94 controlled byvalve 95. Intermediate extract phase from extractor 60 passes by actionof pump I00 through line IIII controlled by valve I02. The intermediateextract phase may then pass through line I03 and valve I04 into coolerI05 and through line I06 into separator I0'I or this equipment may beby-passed by closing valve I04 and opening valve I08. If desired, partof the fiow may be through valve I04 and part through valve I08.

When intermediateextract phase passes through valve I04, its temperatureis sufficiently reduced by cooler I05 to cause phase separation inseparator I01 into an intermediate rejected raffinate and a furtherextract. When a liquid, normally gaseous solvent is employed, chillingmay be accomplished in I 05 by vaporization of at least part of thesolvent with consequent internal refrigeration. This intermediaterejected rafiinate is removed from I0! by pump III] in line IIIcontrolled by valve II2. I prefer to return the intermediate raffinatefrom separator Ill? into that zone of, extractor 60 wherein the oilbeing extracted has substantially the same viscosity gravity constant asthe rejected raffinate being introduced. The viscosity gravity constantof the intermediate rafiinate is usually intermediate that of the finalrafiinate issuing from extractor 60 via line 94 and that of the oilentering extractor 60 by line 51. Consequently, the intermediateraiiinate is preferably introduced into extractor 60 at a pointintermediate the introduction of the incoming oil and the removal of thefinal raflinate. Forthis purpose line III is connected with lines H3,H4, and H5 which are respectively controlled by valves I I6, III, and H8whereby the intermediate rafiinate can be introduced into sections 62,63 and. 64 as desired. Extract phase passes from separator I0'I byaction of pump I20 through line I2I controlled by valve I22. Line I2Iconnects with line IOI.

Extract phase from separator I01 if valve I04 is open, or extract phasedirect from extractor 60 if valve I08 is open, or a mixture of these,passes through line IOI to heater I23 and thence through line I24 intoseparator I25. Sufilcient heat is provided in heater I23 to preferablycause substantially complete vaporization of the solvent from theextract phase. The solvent vapors exit via line I26 controlled by valveI2'I. Extract freed of solvent is removed by action of pump I30 throughline I20 controlled by valve I29 and passes through cooler I3I beforeintroduction into extractor I0 via lines I32 and 38, orifice mixer 39and line 40. Because this extract phase comprises oil characterized byviscosity gravity constant intermediate that of the rafiinate issuingthrough line 22 and that of the oil entering through line I5, I preferto introduce the same at an intermediate point in extractor I0,preferably into that zone wherein the oil being extracted hassubstantially the same viscosity gravity constant as the extract beingintroduced.

In the operation of this apparatus, it is desirable in certain instancesto maintain sections 26 to 28 of primary extractor I0 at successivelydecreasing temperatures, but it is also within the purview of myinvention to maintain these sections at the same temperature or even atsuccessively increasing temperatures. Similarly, sections 6| to 05 ofsecondary extractor may also be at successively increasing or decreasingtemperatures, or at the same temperature.

The solvent employed for the second extraction may be the same as thatused in the primary extraction. In that case, I usually prefer to usehigher temperatures in extractor 60 than in the primary extractor I0,although in some instances the same or a lower temperature than thatprevailing in the primary extraction may be used in the secondextraction.

In order to exemplify the application of my invention to a solventextraction process involving a pure solvent for the first extraction,followed by a modified solvent for the second extraction, 300 volumepercent. liquid sulphur dioxide, based upon the amount of oil enteringvia line I2, is introduced through line H, orifice mixer 48 and line 49.This selective solvent passes countercurrently in primary extractor I0with the incoming oil introduced through line I2, orifice mixer I4 andline I5. This oil may be characterized by a viscosity gravity constantof 0.875. The low grade extract containing the major proportion ofnon-paraffinic fractions and the major proportion of liquid sulphurdioxide is removed from primary extractor I0 through line I9. This lowgrade extract may be characterized by a viscosity gravity constant of0.955. The primary raffinate containing a small proportion of liquidsulphur dioxide constitutes the feed for the second extraction and ischaracterized by a viscosity gravity constant of 0.838. The solventemployed for the second extraction may be modified by one or more of theaforementioned modifying agents; for instance, this solvent may compriseliquid sulphur dioxide, and 30% benzene, and may be used in theproportion of 300 percent. of solvent based upon the oil introduced intothe system through line I2. It is desirable that the high graderaffinate removed via line 94 will contain substantially all of theparafiinic fractions of low viscosity gravity constant, and it is alsodesirable that the fractions characterized by low viscosity gravityconstant present in the intermediate extract removed from the secondextraction via line IOI will be substantially recovered by separationfrom the extract phase. The final raffinate issuing through line 94 mayhave a viscosity gravity constant of 0.810 while that of theintermediate extract passing through valve I02 may be 0.860.

If desired, valve I04 may be entirely closed, in which event all of theintermediate extract phase passes through line IOI into heater I23 andseparator I25, Where the solvent is removed. The extract is then cooledin I3I before introduction into primary extractor I0. This introductionis preferably into that zone of IO where oil of substantially the sameviscosity gravity constant is contained. For instance, if the oilpassing through line I32 has a viscosity gravity constant of 0.860, Iprefer that it be introduced into that portion of extractor I0 whereinthe oil being extracted has substantially similar viscosity gravityconstant as the extract being introduced in order that the equilibriumof the system may be retained.

If the intermediate extract phase from 60 passes through coil I05 andseparator I01, the rejected rafiinate passing through line III may havea Viscosity gravity constant of 0.828, for instance. I prefer that thisrejected rafifinate be returned to that portion of the second extractor60 wherein the oil being extracted has substantially the same viscositygravity constant as the rejected rafiinate. The extract passing throughline IOI, heater I23, line I24, separator I25, line I28, cooler I3! andline I32 to the extractor I0 then may have a viscosity gravity constantof 0.868. I prefer to return this extract to a corresponding portion ofextractor I0 in the above described manner.

As an example of the temperature conditions which may exist in the abovedescribed process, the oil may be introduced into primary extractor I0via line I2 at 95 F. for countercurrent extraction with liquid sulphurdioxide introduced at F. The primary rafiinate thus produced may entersection 65 of column 60 at 80 F. The temperature in '60 may besuccessively increased until the temperature in section 6I is F. Inorder to produce adequate phase separation of the intermediate extractphase in separator I01, this mixture may be lowered to 20 F. Theintermediate extract phase may be heated to 300 F. in I23 to causesubstantially complete removal of sulphur dioxide and benzol inseparator I25.

My invention is capable of many modifications. For instance, extractorsI0 and 60 may be divided into more or fewer sections. Or, in fact, theymay be undivided into sections in which case the oil and solvent canfreely flow up and down the columns. My invention may be additionallymodified by cooling the extract phase passing through line I9 to rejectan intermediate rafiinate and by returning this rejected raffinate tothat zone in extractor I0 containing oil of substantially the sameviscosity gravity constant undissolved in the solvent. Anothermodification may be to subject the oil flowing through line I32 toextraction with a solvent such as liquid sulphur dioxide in an extractorother than extractor I0.

It is to be understood that the foregoing is merely illustrative of thegeneric invention, and the examples are not to be taken as limitationsthereof, as many modifications of my invention may be made Within thescope of the following claims.

I claim:

1. A process for the separation of parai'finic and non-paraffinicfractions from an oil containing the same which comprisescountercurrently extracting said oil with a selective solvent,separating a rafiinate insoluble in said solvent from the extract phase,separating an intermediate raffinate from said extract phase andintroducing said intermediate rafiinate into said extraction at thatzone wherein oil being extracted has substantially the same viscositygravity constant as the intermediate raffinate being introduced.

2. A process for the separation vof parafiinic and non-paraflinicfractions from an oil containing the same which comprisescountercurrently extracting said oil with a selective solvent,separating a raflinate insoluble in said solvent from the extract phase,cooling said extract phase to separate an intermediate raffinatetherefrom and introducing said intermediate rafiinate into saidextraction at a point intermediate the points of introduction ofselective solvent and oil enter-' ing the system.

3. A process for the separation of paraflinic and non-parafilnicfractions from an oil containing the same which comprisescountercurrently extracting said oil with a selective solvent,separating a raifinate insoluble in said solvent from the extract phase,cooling said extract phase to separate an intermediate raflinatetherefrom and introducing said intermediate raflinate into saidextraction at that zone wherein oil being extracted has substantiallythe same viscosity gravity constant as said intermediate raflinate beingintroduced.

4. A process for the separation of paraflinic and non-parafllnicfractions from an oil containing the same which comprises extractingsaid oil with a selective solvent, separating a rafiinate insoluble insaid solvent from the extract phase, extracting said ratfinate with aselective solvent to produce a final rafiinate and an intermediateextract phase, cooling said intermediate extract phase to separate anintermediate rafiinate therefrom, removing the intermediate raffinatefrom the cooled intermediate extract phase, then removing selectivesolvent from said intermediate extract phase by distillation, coolingthe intermediate extract after said distillation and introducing saidcooled intermediate extract into said first mentioned extraction at thatzone wherein oil being extracted has substantially the same viscositygravity constant as said intermediate extract being introduced.

5. A method of contact of oil containing paraffinic and non-parafiinicconstituents with a selective solvent in which phase separation occursto produce a raflinate relatively more paraflinic in character and anextract relatively less paraflinic in character than the original oilwhich method operates in a countercurrent system of contact between theoil and the selective solvent which comprises countercurrentlycontacting said oil with a selective solvent and thereby forming arafiinate phase and an extract phase, separating said phases, coolingsaid extract phase and recovering an oil fraction therefrom, said oilfraction having a viscosity gravity constant which is higher than theviscosity gravity constant of oil fractions contained in said rafiinatephase and introducing said oil fraction recovered from said extractphase into the extraction system at a point intermediate between thepoints of introduction in said countercurrent extraction system of theselective solvent and the oil.

6. A method according to claim 5 in which the fraction recovered fromthe extract phase is introduced into the extraction system at a point insaid extraction system wherein the viscosity gravity constant of the oilfractions present at said point issubstantially the same as theviscosity gravity constant of said oil fraction recovered from saidextract phase.

ULRIC B. BRAY.

